Early subduction dynamics recorded by the metamorphic sole of the Mt. Albert ophiolitic complex (Gaspé, Quebec)

Dubacq, Benoît; Soret, Mathieu; Jewison, Ella; Agard, Philippe

doi:10.1016/j.lithos.2019.03.019

Cited by 20 publications

(23 citation statements)

References 97 publications

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“…These results, and the single observation that the amphibolites are welded to the peridotites of the Andaman ophiolite, are coherent with previously documented metamorphic soles around the world (e.g., Agard et al, 2016). The samples we collected do not witness the highest-grade parts of soles reported elsewhere (~850°C and~1.2 GPa; e.g., Agard et al, 2016;Cowan et al, 2014;Dubacq et al, 2019;Plunder et al, 2016;Soret et al, 2017). This may either mean that these highest-grade parts were not accreted in the Andaman case (not all sole localities show the full sequence) or that it may be present elsewhere below the Andaman ophiolite.…”

Section: Condition Of Formation Of the Sole Of The Andaman Islandssupporting

confidence: 91%

“…They form during subduction initiation (Wakabayashi & Dilek, 2000) over a short time span (typically of 1-2 Myr) and cool coevally to the formation of SSZ ophiolite (Hacker, 1994;Rioux et al, 2016). Worldwide, they share very similar characteristic: they are formed in a warm thermal regime, up to melting condition (850°C and 1.2 Gpa), in a much higher thermal regime than expected for a mature subduction zone (Agard et al, 2016;Dubacq et al, 2019;Jamieson, 1986;Soret et al, 2017;Wakabayashi & Dilek, 2003;Woodcock & Robertson, 1977). They comonly have a 10-to 500-m thickness in total, and parts with different peak metamorphic grades represent different tectonics slices.…”

Section: 1029/2019tc005762mentioning

confidence: 99%

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History of Subduction Polarity Reversal During Arc‐Continent Collision: Constraints From the Andaman Ophiolite and its Metamorphic Sole

et al. 2020

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Subduction polarity reversal during arc-continent collision has been proposed as a key mechanism to initiate new subduction zones. Despite often interpreted, well-exposed geological record that document the reversal is sparse. The ophiolitic lithounits of the Andaman and Nicobar Islands have been proposed to have formed during the initiation of a new subduction zone following the collision of the Woyla Arc of Sumatra with Sundaland (Eurasia). We here present new field, petrological and geochronological data to evaluate the timing of the initiation of Andaman subduction. We targeted the previously inferred but unstudied metamorphic sole of the Andaman ophiolites that witnessed juvenile subduction. Thermodynamic modeling reveals that the exposed amphibolites of the sole formed at around 0.9 GPa and 675°C. We dated two samples of the metamorphic sole using the Ar/Ar method on amphibole, giving cooling ages of 106.4 ± 2.1 and 105.3 ± 1.6 Ma. This is similar to published ages from plagioclase xenocrysts in recent Barren Island volcanics and in zircons from a gabbro sample from the Andaman ophiolite, which we interpret as the age of the original ophiolite formation. The Ar/Ar ages are considerably older than arc magmatic gabbros and plagiogranites of the overlying ophiolite previously dated at 99-93 Ma and thought to reflect the ophiolite age but recently reinterpreted as a volcanic arc built on the ophiolite. Combined with the ages of Woyla-Sundaland collision, we argue that subduction polarity reversal occurred in a transient period of perhaps some 10 Myr, similar to recent settings.

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Section: Condition Of Formation Of the Sole Of The Andaman Islandssupporting

confidence: 91%

Section: 1029/2019tc005762mentioning

confidence: 99%

History of Subduction Polarity Reversal During Arc‐Continent Collision: Constraints From the Andaman Ophiolite and its Metamorphic Sole

et al. 2020

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“…Our group has studied these tectonic environments across a variety of locations (Oman, Turkey, New Caledonia;Canada;e.g., respectively, Agard et al, 2016;Plunder et al, 2016;Soret et al, 2016;Dubacq et al, 2019). The present study combines information from both sides of the plate interface, focusing in part on the works of M. Soret and C. Prigent in Oman-UAE (Soret et al, 2017(Soret et al, , 2019Prigent et al, 2018a,b,c).…”

Section: J O U R N a L P R E -P R O O Fmentioning

confidence: 93%

“…At mineral scale, evidence must be looked for in the hottest and best-preserved granulite facies samples, since they were subtracted from the slab just before, i.e., as close as possible to the point of deep coupling. In Mt Albert, HTa samples exhibit a compact framework with nearly equant textures and relatively constant and coarse grain size (Dubacq et al, 2019; Fig. 13a).…”

Section: Deformation Mechanisms and Element Transfer Across Sole\perimentioning

confidence: 99%

Slabitization: Mechanisms controlling subduction development and viscous coupling

Agard

Prigent

Soret

et al. 2020

Earth-Science Reviews

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This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

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“…The crystallization temperature of each generation of chlorite in 23 selected samples was estimated using the Chl–Qz–H 2 O thermodynamic model of Vidal et al () from element abundances at a reference pressure of 3 kbar and H 2 O activity at fixed unit value. The absolute uncertainty on the crystallization temperature estimates is ~50°C (Dubacq, Soret, Jewison, & Agard, ; Vidal et al, ), although the relative uncertainty between samples is likely lower (10–20°C). The semi‐empirical thermometer of Bourdelle, Parra, Beyssac, Chopin, and Vidal () formulated for low‐ T chlorite was used for comparison.…”

Section: Analytical and Computational Methodsmentioning

confidence: 99%

Pre‐orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees

Airaghi

Bellahsen

Dubacq

et al. 2020

Journal Metamorphic Geology

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Pre-kinematic greenschist facies metamorphism is often observed in granites and basement units of mountain belts, but rarely dated and accounted for in orogenic cycle reconstructions. Studying pre-kinematic alteration is challenging because of its usual obliteration by subsequent syn-kinematic metamorphism often occurring at conditions typical of the brittle-ductile transition. It is, however, to be expected that pre-kinematic alteration has major implications for the rheology of the upper crust. In the 305 Ma-old Variscan basement of the Bielsa massif (located in the Axial Zone of the Pyrenees), successive fluid-rock interaction events are recorded in granites below 350°C. Combined microstructural and petrographic analysis, low-T thermobarometry and in situ U-Th/Pb dating of anatase, titanite and monazite show extensive pre-orogenic (pre-Alpine) and pre-kinematic alteration related to feldspar sericitization and chloritization of biotite and amphibole at temperatures of 270-350°C at 230-300 Ma. This event is followed by a second fluid-rock interaction stage marked by new crystallization of phyllosilicates at 200-280°C and is associated with the formation of mylonitic shear zones and fractures parallel to the shear planes. U-Pb anatase and monazite ages as well as the microtextural relationships of accessory minerals suggest an age for this event at 40-70 Ma, consistent with independent regional geology constraints. The Variscan basement was therefore softened at late to post-Variscan time, at least 150-200 Ma before the main Alpine shortening while Alpine-age compression (c. 35-50 Ma) leads to the formation of a dense net of mylonites. The associated deformation, both distributed at the scale of the Bielsa massif and localized at decametric scale in mylonitic corridors, precedes the strain localization along the major thrusts of the Axial Zone. The Bielsa massif is a good example where inherited, pre-orogenic upper crustal softening controls the deformation patterns in granitic basement units through low-grade metamorphic reactions. K E Y W O R D SAxial Zone, Bielsa, chlorite-white mica thermobarometry, mylonites, U-Th/Pb anatase-titanitemonazite dating 184 | AIRAGHI et Al.

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Early subduction dynamics recorded by the metamorphic sole of the Mt. Albert ophiolitic complex (Gaspé, Quebec)

Cited by 20 publications

References 97 publications

History of Subduction Polarity Reversal During Arc‐Continent Collision: Constraints From the Andaman Ophiolite and its Metamorphic Sole

History of Subduction Polarity Reversal During Arc‐Continent Collision: Constraints From the Andaman Ophiolite and its Metamorphic Sole

Slabitization: Mechanisms controlling subduction development and viscous coupling

Pre‐orogenic upper crustal softening by lower greenschist facies metamorphic reactions in granites of the central Pyrenees

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